introduction · introduction andrews who is the first one studied normal occlusion in 120 cases...
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introduction
Normal occlusion
Range Closing up
introduction
Andrews who is the first one studied normal
occlusion in 120 cases with the following
criteria:
1. Correct bite
2. Did not have orthodontic treatment
3. Straight teeth and pleasing appearance
Andrews described six keys to normal occlusion:
1. Molar relationship.
2. Crown angulation (tipping).
3. Crown inclination (torque).
4. Absence of rotation.
5. Tight contact.
6. A flat occlusal plane or slight curve of Spee.
Key I. molar relationship
Key I. molar relationship
The mesiobuccal cusp of the upper first molar
should occlude within the mesiobuccal groove of
the lower first molar.
The mesiolingual cusp of the upper first molar
should occlude in the central fossa of the lower
first molar.
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The crown of the upper first molar must be
angulated so that its distal marginal ridge
occludes with the mesial marginal ridge of the
lower second molar.
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• Molars and premolars
cusp embrasure buccally
cusp fossa lingually
• The tip of ,maxillay canine occlude slightly
mesially to the embrasure between lower canine and premolar ( canine rise concept)
Key II. Crown angulation (tipping)
It’s the mesiodistal tip of the long axis of the
crown
Angle formed between the long axis of the
crown and perpendicular line erected from the
occlusal plane (mesiodistal view)
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The gingival part of the long axis of the crown
must be distal to the occlusal part of the axis.
(Positive angulation)
The gingival part of the long axis of the crown
must be distal to the occlusal part of the axis
(positive) and vice versa
In normal occlusion, the crown angulation was
positive for all teeth
Key III. Crown inclination (torque)
It’s the faciolingual inclination of the long axis
of the crown
Its angle formed between the facial long axis of
the crown and a perpendicular to the occlusal
plane. (viewed from proximal surface)
When the gingival portion of the long axis of the crown
is lingual to the incisal portion , the crown inclination
is positive.
(and vice versa)
In normal occlusion, the crown inclination for all teeth
was negative except maxillary central and lateral
incisors
•Lingual crown inclination was similar in maxillary
canines and premolars, and more pronounced in the
maxillary molar
•Lingual crown inclination progressively increased from
mandibular canine through the mandibular second
molars.
Key IV. rotations
In normal occlusion, the dentition should be
free from undesirable rotations.
If the molar rotated, it would occupy more
space than normal within the arch.
The reverse is true for the anterior teeth.
Key V. tight contact
In normal occlusion, contact area should be
tight.
Key VI. Occlusal plane
Occlusal plane: is the imaginary plane on which
the teeth meet in occlusion.
In normal occlusion, the occlusal plane should
be flat or nearly flat.
Deep curve of Spee, result in a more confined
area for the maxillary teeth
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Goals of functional occlusion (ROTH)
• Coincident centric relation and occlusion
• Cusp embrasure relationship buccally
• Cusp fossa relationship palatally
• Equal posterior forces along teeth long axis
• There should be 0.005 inch (0.13mm) space between
the anterior teeth when posterior teeth in occlusion
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Goals of functional occlusion
• In protrusive movement, anterior guidance
produces posterior disocclusion.
• In lateral movement, canine serve as the main
guiding inclined surface ( canine guidance).
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